Here was the exact answer on Andrew's website describing it in his own
words:

Andrew Gower, 1998 (click image)

Devious Mud was the precursor to Runescape
and it was made by Andrew Gower, co-founder of Jagex. He wrote it whilst he was at University at Cambridge. It was released
for one week as a beta but was then closed almost as swiftly as it had been released. Very few people played it
because the game itself was only released on Andrew's personal website (which few people visited), and since Andrew had
not founded Jagex, there were no "Admins" or "Mods" as such. The only known list of people who possibly played
the game are: Merlin, Andrew,
Paul, Lightning, gugge, rab. As a result, only three screenshots exist of the actual game, although Andrew
himself probably has a few more hidden away.

Screenshots:

Here are the three screenshots that currently exist showing
Devious Mud. It is clear to see that the graphics are very old but related to the graphics seen on runescape classic. However,
because so few people played this game, general interest in the game has slowly increased out of curiosity.

As you can see, it is clear that the idea of runescape did indeed originate
from Devious Mud. You can see from the menu bar that the words "examine", "take" and "use" are used
in Runescape to interact with every element of the game. The graphics are remarkably similar to the graphics at the start
of Runescape classic, but with newer technologies available to Jagex, the graphics slowly improved and are now vastly different
from the graphics seen in Devious Mud. Despite this, people still want to play the game because it is still considered "The
First Runescape", but it has never been re-released to the public.